Control for luminaires employing gaseous discharge lamps at low ambient temperatures



N 1970 w. F. BLACKFORD 3,

CONTROL FOR LUMINAIRES EMPLOYING GASEOUS DISCHARGE LAMPS AT LOW AMBIENTTEMPERATURES Filed May 22, 1968 III/VENTUR- Z/QZZGQS E Black/0m 'U.s.cl. 315-118 United States Patent EMPLOYIN G AT LOW ABSTRACT OF THEDISCLOSURE A light sensitive control device for gaseous discharge lampshaving normally closed switch means for controlling the power into thegaseous discharge lamps, light sensitive circuit means for opening thenormally closed switch means when the ambient light level reaches apreselected level, and temperature responsive means for disabling thelight sensitive circuit means when the ambient temperature goes below apreselected level.

BACKGROUND OF THE INVENTION The invention pertains to the fieldphotosensitive devicesfor the control of lighting equipment and, moreparticularly, to the control of gaseous discharge lightingdevices at lowtemperatures.

The starting voltage required to initiate an electrica discharge througha gaseous discharge lamp increases as the ambient ternperaturedecreases. In the case of mercury and fluorescent lamps, industrystandards give start- :ingvoltage requirements attemperature as low as-20 F -but not below this temperature. In discharge lamps,utilizingmercury vapor as the conducting medium, starting of such lampsat temperatures below the freezing point of mercury (38.83 F.) isextremely diflicult In areas where the temperature is likely to falltoyery low temperatures and where it is desired to utilize gas eousdischarge lamps as light sources, this has sometimes been accomplishedby energizing the luminaires ,inthe fall of the year before thetemperature gets'extremel'y low and keeping them energized until late inthe winter when the temperature. at the usual starting time of the dayhas risen to temperatures warmer than 20 F.

Where outdoor lighting circuits are controlled by a manual switch, theabove procedure is reasonably feasible. However, where an outdoorlighting circuit or individual luminaires are controlled byphotoelectric controls which turn on and turn oil the electrical powerat predetermined light levels, it has been necessary in the past for thecontacts of these photoelectric controls to be bypassed or the controlshooded when it is desired to keep the lights energized continuouslyduring extremely cold weather.

SUMMARY OF THE INVENTION The invention as hereinafter describedovercomes the aforedescribed ditficulties by disabling the photoelectriccontrol whenever the ambient temperature falls below a predeterminedlevel. This is accomplished by inserting a thermostatic switch in thecontrol circuit to interrupt the power to the photoelectric control whenthe ambient temperature drops below the preselected value. Thephotoelectric control is thereby disabled from opening normally closedcontacts which carry power to the luminaire. After the ambienttemperature rises to a value at which the gaseous discharge lamp can bestarted by its associated ballast, or in other words, a temperaturevalue at which the output voltage of the ballast is sufficient to startthe discharge device, the contacts of the thermostatic device 3,539,861Patented Nov. 10, 1970 ICC close to energize the photoelectric controlwhich then takes over the normal tum-on and turn-off functions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 schematically illustrates anelectrical circuit for a gaseous discharge type lighting device whichcircuit includes control means incorporating the present invention; and

FIG. 2 illustrates a modification of the circuit shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS vices, such as mercury vaporlamp 2 and its associated ballast 5, are well known to those skilled inthe art, and details of construction thereof form no part of the instantinvention.

Ballast 5 receives its input from a conductor 6 and a conductor 7.

Mercury vapor lamp 2 and ballast 5 may be housed within a luminairehousing indicated by the dashed line enclosure 8.

Alternating current power is placed across conductor 7 and conductor 9.The flow of power from conductor 9 to conductor 6 is controlled by aphotoelectric and tem 'perature sensing circuit housed within a housing10 indicated in dashed lines. The photocell housing may be of a plug-invariety mounted on luminaire housing 8.

' The control circuit power is obtained through a circuit completed toconductor 7 through a conductor 11. The power to ballast 5 is conductedfrom conductor 9 to conductor 6 through normally closed contacts 12 of arelay 13. The current required for the energization of the operatingcoil of relay 13 is obtained through a circuit comprising conductor 11,a current limiting resistor 14, a conductor 15, contact 16 of athermostatic switch 17, a photocell 8 and a rectifying bridge 19. Theother input terminal of rectifier bridge 19 is connected to conductor 9.A spark gap device 20 is connected between conductor 9 and conductor 15for suppression of high voltage transients and protection of the controlcircuit.

The photocell 18 is mounted within housing 10 adjacent to an ambientlight admitting opening 21.

The thermostatic device 17 is mounted within an extension 22 of housing10 to thermally isolate thermostatic device 17 from the other elementsof the control circuit and thereby give a more accurate reading ofambient temperature.

In order to better thermally isolate thermostat 17, it may be placedoutside of housing 10 and mounted remotely from housing 10 and housing 8as shown in FIG. 2. In that construction, contact 16 of thermostat 17 isplaced between conductor 7 and resistor 14, and conductor 15 isconnected directly to photocell 18.

If we assume that the ambient temperature is sufficiently high tomaintain contact 16 closed, the photosensitive control circuit willoperate in a normal manner in response to ambient light levels. When theambient light level is low, contact 12 will remain closed to supplypower to ballast 5. When the ambient light level rises to a preselectedlevel, photocell 18 becomes sufficiently conductive that the DC. currentfrom bridge 19 energizes relay 13 to open contcat 12 and thereby turnoff lamp 2. As previously explained, when the ambient temperature dropsto extremely low levels, difiiculties in starting lamp 2 may beexperienced and it is then desirable to keep lamp 2 on continuouslyuntil the ambient temperature rises to a level where the output voltageof ballast 5 is sufiicient to start lamp 2. When the ambient temperaturedecreases to such a level, thermostat 17 opens contact 16 to de-energizethe photoelectric control circuit. Contact 12 will then remain closed tomaintain lamp 2 energized. Since contact 16 is inserted in the controlcircuit only and does not carry the power used to energize lamp 2,contacts 16 may have a relatively small power rating and thermostat 17may be of a relatively inexpensive variety. An economy in theconstruction of the control is thereby effected.

While the heretofore described embodiments of the invention areeifective to accomplish the objects of the invention, it is not intendedthat the invention be confined to the illustrated embodiments, sincethey are adapted to modification Without departing from the scope of theappended claims.

I claim: 1. In a control system for outdoor lighting apparatus:electroresponsive means for turning power on and 01? to lamp means, saidelectroresponsive means having a normal condition in which power isturned on to said lamp means, and said electroresponsive means beingenergizable to turn said power off; light responsive control meanssensitive to the ambient light intensity level in the area of saidlighting apparatus for energizing said electroresponsive means to turnoff said lamp means when said light intensity is above a preset level; I

power source means for supplying the electrical power to said lightresponsive control means; and temperature responsive control meansconnected in a circuit in parallel with said power source means andsensitive to the ambient temperature in the area of said lightingapparatus for interrupting said electrical power to said lightresponsive control means when said ambient temperature falls below apreselected temperature;

whereby said lamp means remains energized when said ambient temperaturefalls below said preselected temperature.

4 2. The invention as defined in claim 1 in which said lamp meanscomprises a gaseous discharge lamp.

3. The invention as defined in claim 1 in which said lamp comprises amercury vapor lamp.

4. The invention as defined in claim 1 together with: a housing for saidlight responsive control means; and an extension from said housing forhousing said temperature responsive control means. I 5. The invention asdefined in claim 1 together with .a housing for said light responsivecontrol means, said temperature responsive control means being mountedexteriorly to said housing.

6. The invention as defined in claim 1 in which said electroresponsivemeans comprises a relay with normal contact means for carrying power tosaid lamp means.

7. The invention as defined in claim 5 in which said temperatureresponsive control means is mounted remotely from said housing and saidlamp means.

8. Outdoor lighting apparatus including a power source, switch contacts,ballast and a lamp in a primary circuit, the improvement being a secondcircuit in parallel with said power source and comprising in series.

a relay coil for activating said switch contacts in said primarycircuit;

a light control for activating said relay coil; and

a thermostatic device for activating said primary circuit intocontinuous operation when the ambient temperature drops below apredetermined level.

9. The invention as defined in claim 8 in which said switch contacts arenormally closed.

10. The invention as defined in claim 8 in which said light control is aphotocell that is responsive to the ambient light intensity.

8/1968 Zerfoss 315-159 X JAMES W. LAWRENCE, Primary Examiner C. R.CAMPBELL, Assistant Examiner US. Cl. X.R. 315-159; 282

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 539861 November 10 1 Wallace F. Blackford It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 4 line 15, before "contact" insert closed Signed and sealed this6th day of April 1971.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WILLIAM E. SCHUYLER Attesting OfficerCommissioner of Pat:

